The standard telecast in Japan uses the NTSC system. Recently, however, a higher-quality telecast system represented by hi-vision is developed and gradually spread. In the case of the NTSC system, the number of scanning lines is set to 525 and the aspect ratio is set to 4:3. In the case of the hi-vision system, however, the number of scanning lines is set to 1,125 and the aspect ratio is set to 16:9. Therefore, when using the hi-vision system, it is possible to enjoy realistic pictures having higher resolution.
To display a picture according to the NTSC system on a television receiver according to the hi-vision system, it is necessary to convert an SD (Standard Definition) signal corresponding to a video signal according to the NTSC system into an HD (High Definition) signal corresponding to a higher-resolution video signal. Hereafter, a signal before converted into more number is properly referred to as an SD signal, SD data, or an SD pixel and a signal after converted into more number is referred to as an HD signal, HD data, or an HD pixel.
Conversion of the SD signal into the HD signal has been performed by simple interpolation in the horizontal direction and vertical direction.
However, because the interpolation is performed by a cascaded FIR filter, the resolution of an HD signal is the same as that of an original SD signal. When a normal picture is used as a conversion object, the resolution of an HD signal is inferior to that of an SD signal due to conversion loss in a static picture section because the vertical interpolation is performed through in-field processing but inter-field correlation is not used.
Therefore, the applicant proposed in Japanese Patent Application No. 6-205934 a system of performing class division in accordance with a three-dimensional (space-time) distribution at a picture signal level serving as an input signal and operating an optimum estimated value as an HD signal by using a predicted coefficient previously obtained through learning for each class.
However, though a high-resolution picture can be obtained by processing both luminance signal and color signal by the above proposed system, problems occur that the capacity of a ROM for storing coefficient increases, an apparatus increases in size and moreover, the cost increases.